1. Field of the Invention
The present invention relates to vehicle driving systems and more particularly, to a driving system for electric vehicle, which uses a clutch switching unit to control a motor rotor-driven bushing in rotating a wheel hub via a direct-drive active clutch or via a set of planet gears and a reducing clutch. At the initial state after startup of the motor, the direct-drive active clutch runs idle, enabling the wheel hub to provide a low-speed high-torque output, saving power consumption. When the vehicle speed reaches a predetermined level, a control circuit drives a clutch motor to move the clutch switching unit in releasing the reducing clutch to idle the planet gears, enabling the direct-drive active clutch to be switched on so that the rotor of the motor can rotate the wheel hub directly to accelerate the vehicle speed.
2. Description of the Related Art
FIG. 11 illustrates a conventional driving system used in an electric vehicle. According to this design, the driving system comprises a motor 9 and a transmission mechanism 91. The transmission mechanism 91 comprises a driving wheel set 911 rotatable by the motor 9, a transmission wheel set 912, a transmission belt 913 coupled between the driving wheel set 911 and the transmission wheel set 912 for enabling the transmission wheel set 912 to be rotated by the driving wheel set 911, an output shaft 914 that is rotatable by the driven wheel set 911 to rotate a reducing mechanism 915 and a wheel hub 916, and a clutch 92.
The transmission wheel set 912 comprises a main transmission wheel 9121 and a sliding transmission wheel 9122. The clutch 92 controls displacement of the sliding transmission wheel 9122 subject to a centrifugal force to change the transmission radius of the transmission belt 913, achieving transmission and speed reducing.
According to the aforesaid design, the motor 9 drives the driving wheel set 911 to rotate the transmission wheel set 912 by means of the transmission belt 913, enabling the output torque to be transferred to the reducing mechanism 915 and then the wheel hub 916. By means of friction, the transmission belt 913 transfers the rotary driving force from the driving wheel set 911 to the transmission wheel set 912. This friction transmission consumes much electric power. Further, after transmission of the rotary driving power from the driving wheel set 911 to the transmission wheel set 912 through any transmission measure, the reducing mechanism 915 reduces the output speed. Thus, the motor 9 cannot perform efficiently and consumes much electric power during operation. Thus, an electric vehicle using this design of driving system is not practical for long distance application.